# Homework Help: 2 Electric Charge Particles w/ acceleration?

1. Jan 30, 2005

### CinderBlockFist

Hi all, I am having trouble on where to start w/ this problem:

Two equally charged particles, held 3.0 10-3 m apart, are released from rest. The initial acceleration of the first particle is observed to be 7.0 m/s2 and that of the second to be 10.0 m/s2. The mass of the first particle is 6.3 10-7 kg.
(a) What is the mass of the second particle?
_____kg
(b) What is the magnitude of the charge of each particle?
_____C

2. Jan 30, 2005

### MathStudent

Hint:
Use Newton's second and third laws, if you don't know them look them up in your book.
come back if you get stuck

-MS

3. Jan 30, 2005

### CinderBlockFist

Thanks math student. Ok this is what i got so far, I'm not sure if I am approaching it correctly.

I used F=ma for the first particle.

F = (6.3 x 10 ^-7)(7.0 m/s^2)

I got F = 4.41 x 10^-6 N

So, using Coulomb's Law I set this F

F = k (q^2/(3.0 x 10 ^ -3)^2) since both charges are the same.

I get q = 6.643 x 10 ^ -11

Is this the correct approach? I am not sure if I can use F_net = ma for the first particle because I am not sure if that is the net force on the whole system.

4. Jan 30, 2005

### CinderBlockFist

am I supposed to add the accelerations of particles 1 and 2, when i use F_net = ma?

5. Jan 30, 2005

### MathStudent

looks good so far,
since they didn't give you any other info, you can assume that what they gave you makes up the whole system. The only other forces that could be acting in this scenario is gravity, but this is usually negligible so can be ignored.

Now all you need is the mass of the second particle, any ideas?

6. Jan 30, 2005

### CinderBlockFist

Cool, I just plugged in F=ma using the acc. of particle 2. Thanks MS!! for the quick response!

7. Jan 30, 2005

### MathStudent

No... Newton's second law is used for analyizing the motion of one body.

8. Mar 1, 2011

### swanny10

but that doesnt get you the right answer